The present invention relates to a solid-state actuator which deforms upon reception of a voltage and, more particularly, to an ink jet head which injects ink using deformation of the solid-state actuator.
Generally, in an ink jet head of this type, a base plate is formed by a solid-state actuator which deforms in response to reception of a voltage. A plurality of ink chambers with nozzle holes are formed in this base plate. When a voltage is applied, the base plate deforms to expand/contract the ink chambers, and ink is injected from the nozzle holes.
FIG. 4 shows an ink jet head disclosed in U.S. Pat. No. 5,471,231. In FIG. 4, grooves are formed in the upper surface of a base plate 2 consisting of a piezoelectric material to form long groove-like channels 61 to 65 partitioned by partition walls 31 to 36. Electrodes 41 to 45 of a conductive material are formed on the inner walls and bottom surfaces of the channels 61 to 65, respectively. A nozzle plate forming one end face of each of the channels 62 and 64 along the longitudinal direction has nozzle holes 52 and 54. The channels 62 and 64 serve as ink channels while the channels 61, 63, and 65 are dummy channels.
The upper opening portions of the channels 61 to 65 are covered with a cover 4 fixed to the base plate 2 with adhesive portions 5. Each of the ink channels 62 and 64 forms an ink chamber together with the cover 4 and the nozzle plate. The other end face of each of the ink channels 62 and 64 constituting the ink chambers along the longitudinal direction is connected to a common ink reservoir (not shown), so the ink channels 62 and 64 are filled with ink.
In this arrangement, in the partition walls 32 to 35 on both sides of the ink channels 62 and 64, polarizations 91 are formed in advance toward the ink channels in the direction of thickness of partition walls. In addition, a polarization 92 is formed in the base plate 2 in the direction of thickness toward the ink channels in advance.
When a negative potential with respect to that at the electrodes 41 and 43 is applied to the electrode 42, the partition walls 32 and 33 deform in the expansion/contraction mode due to interaction between lines of electric force 81 and the polarization 91. The width and height of the ink channel 62 reduce in accordance with deformation of the partition walls 32 and 33. Since the sectional area of the ink channel 62 reduces, an ink droplet is ejected from the nozzle hole 52. The bottom portion of the ink channel 62 of the base plate 2 also deforms in the expansion/contraction mode due to interaction between lines of electric force 82 and the polarization 92, so the channel bottom portion becomes narrow.
As described above, the ink droplet ejection performance is determined by deformation of the partition walls 32 to 35 and the bottom portions of the ink channels 62 and 64. The same operation as described above is also performed in the ink channel 64 and the partition walls 34 and 35.
In the above-described conventional ink jet head, ink is selectively ejected from the nozzle hole 52 while ink ejection from the nozzle hole 54 is stopped in accordance with the print pattern. In this case, a negative potential with respect to that at the electrodes 41 and 43 is applied to the electrode 42 while the same potential as that at the electrodes 43 and 45 is applied to the electrode 44. For this reason, the electrode 42 has a negative potential with respect to the electrode 44.
The ink channels 62 and 64 are connected to the common ink reservoir (not shown), as described above. With this arrangement, an electric field is generated through a route: ink channel 64.fwdarw.ink reservoir.fwdarw.ink channel 62, and the current leaks. If this potential is continuously applied, the ink is electrolyzed at the electrodes 42 and 44 to form bubbles. When the ink chambers 62 and 64 are filled with bubbles, ink ejection from the nozzle holes 52 and 54 is impeded.